Thermographic duplicating process



April 1, 1969 D. A. NEWMAN 3,

THERMOGRAPHIC DUPLICATING PROCESS Filed Oct. 15. 1965 H El MASTER SHEETINVENTOR.

DOuQZcLSfi. Newman B W M RM fiTTOEA/EYS United States Patent Ofice3,436,293 Patented Apr. 1, 1969 3 436,293 THERMOGRAPHIC DUPLICATINGPROCESS Douglas A. Newman, Glen Cove,,N.Y., assiguor to Columbia Ribbonand Carbon Manufacturing Co., Inc., Glen Cove, N.Y., a corporation ofNew York Filed Oct. 15, 1965, Ser. No. 496,527 Int. Cl. B41m 5/26 US.Cl. 156-240 9 Claims ABSTRACT OF THE DISCLOSURE A thermographicduplicating process in which infrared radiation-absorbing images presenton a plastic film master sheet are reproduced on a succession of copysheets. The unimaged side of the master sheet is smooth and imperviousand accepts wax imaging composition in areas corresponding to theoriginal images and cleanly releases such composition to a copy sheetunder the effects of heat, so that the master can be reimaged to produceas many copies as desired.

The duplicating process of this invention is characterized as a directthermographic process and employs a true thermographic master sheet asopposed to a thermographically-imaged master sheet which relies uponconventional duplicating processes for the production of multiple copiestherefrom.

In the conventional thermographic process for imaging duplicating mastersheets, an original sheet bearing infared radiation-absorbing images issuperposed with a transfer sheet carrying a layer of heat-transferableduplicating composition and a master sheet and the superposed sheets areexposed to infrared radiation. The radiation heats the original imagesto generate a heat pattern which is conducted to the transfer layer,causing transfer thereof to the master sheet in the heated areas. Themaster sheet, which is either a hectograph master or a planographicplate, is then used in either the hectographic or planographic processesto produce multiple copies.

Aside from having the disadvantage of requiring the use of a secondexpensive duplicating system, these known thermographic master-imagingprocesses have an inherent disadvantage which limits the quality of copywhich can be produced. These processes require that either the infraredradiation must penetrate the master and transfer sheets to reach theoriginal sheet, in the case of the reflex method, or that the heatgenerated by the original images must pass through the master sheet toreach the transfer sheet, in the shoot-through method. In either case,some of the radiation and heat is reflected and dissipated so that theoutline of the images transferred to the master is broader and lesssharp than the outline of the original images.

It is the object of the present invention to provide. a truethermographic duplicating process for the imaging of a master sheetwhich subsequently images numerous copies, all under the effects ofinfrared radiation.

It is another object of this invention to provide a thermographicduplicating process in which a great number of copies of originalsubject matter can be produced, each copy having better qualities ofsharpness and clarity than heretofore possible with known thermographicprocesses.

These and other objects and advantages of the present invention will beclear to those skilled in the art in the light of the followingdescription, including the drawing, in which:

FIGURE 1 is a diagrammatic cross-section, to an enlarged scale, of amaster sheet and a transfer sheet superposed and ready for exposure toinfrared radiation against the original images, the sheets beingseparated for purposes of illustration.

FIG. 2 is a diagrammatic cross-section, to an enlarged scale, of themaster sheet imaged according to FIG. 1 and superposed with a copy sheetready for exposure to heat or infrared radiation, the sheets beingseparated for purposes of illustration.

FIG. 3 shows the sheets of FIG. 2 after exposure and separation,illustrating the complete transfer of images 23 from the master sheet tothe copy sheet.

FIG. 4 is a diagrammatic illustration of an apparatus for the continuousproduction of multiple copies of an imaged master sheet according to thepresent invention.

The objects and advantages of the present invention are accomplished bythe present process in which special plastic film master sheets andspecial transfer compositions are used for the thermographic formationof sharp, clear duplicate images on the surface of the master sheetopposite to the carrying the original images, and for the thermographicretransfe-r of such duplicate images to a copy sheet to form sharper andclearer duplicate copies of the original images than heretoforepossible. The master sheet is reimaged and the new images areretransferred as often as necessary to produce as many copies of theoriginal subject matter as maybe required.

One of the important advantages of the present invention is the factthat the present master sheets are not damaged in the present processand may be stored and reused from time to time as necessary to provideas many copies as may be desired at any given time.

The most important advantage of this process is the quality of the copyproduced. The excellence in quality is due to the fact that the originalimages are exposed directly to the radiation source, and the transfercomposition is in intimate surface contact with the master sheet. Thusthere is no opportunity for the infrared radiation to be dissipated orreflected by other sheets prior to :being absorbed by the originalimages, nor is there any opportunity for the heat generated in themaster sheet to be dissipated by other sheets prior to being conductedto the transfer composition. In this manner the amount of dis tortioncaused by dissipation and reflection is kept to a minimum.

The invention is best described by reference to the accompanyingdrawing. As shown by FIG. 1, a master sheet 10 comprising a flexibleplastic film foundation 11 having a special release surface 13 isprovided on the opposite surface with infrared radiation-absorbingimages 12. The master sheet is superposed with its release surface incontact with the heat-transferable layer 22 of a transfer sheet 20having a flexible foundation 2-1.

In this first step the images 12 are exposed directly to an infraredradiation source to heat the images, the underlying areas of the masterfoundation and the contacting portions of the transfer layer to causesoftening and melting of the portions of the transfer layer in areascorresponding to the location of the original images. These meltedportions of the transfer layer adhere to the release surface of themaster and transfer thereto in the form of images 23 when the master andtransfer sheet are separated.

In the next step, shown by FIG. 2, the dual-imaged master is superposedwith a copy paper 30, so that the images 23 are in contact with thesurface of the copy paper and heat is applied to cause the images 23 toagain soften and melt and adhere to the surface of the copy sheet. Uponseparation of the sheets the images 23 transfer substantially completelyto the copy paper as images 24 which are sharp, clear duplicates oforiginal images 12.

In this second step, heating of the images 23 may be caused by anoverall heating of the sheets, such as by passing them between heatedrollers or pressing them against a heated platen, or by mean ofselective heating caused by exposing the sheets to infrared radiation toagain heat the original images and the underlying images 23.

Since one of the important advantages of the present process is theavoidance of the necessity of using a separate duplicating process, uchas hectography or planography, the present process lends itself verywell to a continuous operation on a single apparatus in which the twotransfer operations are carried out and repeated as often as necessaryin continuous sequence to produce the desired number of copies.

One such continuous operation is shown by FIG. 4 in which the originalsheet is mounted on a transparent drum 50 which may be a cylinder ofclear plastic such as polystyrene which does not absorb infraredradiation to any substantial extent. The drum is provided with infraredradiation lamps 51 and 52. The transfer sheet and copy paper are presentas continuous rolls. The transfer sheet is unwound from supply roll 25,passes over tension roller 26 and against the release surface of themaster sheet and over tension roller 27 and is taken up on take-up roll28. The copy paper 30 is unwound by supply roll 31, passes over tensionroller 32 and against the imaged release surface of the master sheet andthen over tension roller 33 and is taken up on take-up roll 34 forsubsequent cutting into sheet lengths.

In operation, the master sheet is attached to the drum 50, such as bymeans of a clamp, adhesive tape or the like, so that images 12 areagainst the drum. As the drum rotates, the master sheet is compressedbetween the drum and the transfer sheet coating 22 since the transfersheet is under tension. The transfer sheet and master sheet move withthe drum past infrared radiation lamp 51 whereby portions of thetransfer layer are melted and adhere to the master sheet in areascorresponding to the location of the original images. A the master sheetand transfer sheet part, the bonded portions of the transfer layertransfer to the master sheet as images 23.

In the second step, the dual-imaged master is rotated into compressionbetween the drum and the copy paper 30 which is under tension. Thecompressed sheets are transported past infrared radiation lamp 52 whichcauses heating of the original images and remelting of images 23 insurface contact with the copy paper. A the master sheet and copy paperare parted, the images remain adhered to and transfer to the copy paperas duplicate images 24.

Obviously take-up roll 34 may be replaced with a cutting means forcutting the continuous copy web into lengths, each sheet being an exactduplicate of the master sheet, or the continuous copy paper web may bereplaced with sheet lengths of copy paper.

The present process may be carried out using precut copy sheets by meansof any commercially-available infrared radiation-exposure apparatus,such as a Thermo- Fax machine. This is accomplished by passing thesuperposed master and transfer sheet through the machine in the ordershown by FIG. 1, and then passing the dualimaged master and a copy paperthrough the machine in the order shown by 'FIG. 2. Both of theseoperations are repeated for each copy which is desired.

The master sheets which are useful for carrying out the present processare thin plastic films which will dissipate a minimum amount of the heatgenerated in the original images. The master sheet is preferablytranslucent, except in cases where it is provided with a layer ofinfrared radiation-reflective material such as a vacuum-depositedmetallic layer as taught by copending application, Ser. No. 57,794,filed Sept. 22, 1960, now United States Patent No. 3,230,874. Thislatter embodiment is important in cases where it is desired to useinfrared radiationabsorbing transfer compositions to producethermographically-reproducible copies and/or magnetically-sensiblecopies containing magnetic iron oxide pigment.

The most critical feature of the present master sheets is the surface ofthe master opposite to that carrying the original images. This surfaceis characterized as a release surface in that it has the ability ofsubstantially completely releasing the images 23 to the copy paper underthe effect of heat. While this function depends to some extent upon thenature of the transfe composition and the copy paper surface, it hasbeen found that the release surface must be one which is non-porous andwill not absorb the melted transfer composition. In this regard, smoothplastic films perform very well as the master sheet. Likewise aninfrared radiation-reflective vacuum-deposited metallic layer on aplastic film master sheet performs very well as a release surface.

Suitable master sheets include thin plastic films such as cellophane,polyethylene terephthalate polyester, tetrafiuoroethylene, polyethylene,cellulose acetate, polyvinyl chloride, polyvinyl fluoride and the like.The essential requirement in each case is that the surface of the filmmust be exceptionally smooth and impervious to the melted transfercomposition.

The transfer compositions useful according to this invention are thosewhich have sharp and relatively low melting points. The transfercompositions are based upon wax binder materials, or mixtures of wax andresinous materials, and contain a coloring material such as a pigment ordyestuff which generally is a material which does not absorb infraredradiation to any substantial degree. However, infraredradiation-absorbing colorants such as carbon black and magnetic ironoxide may be used provided that an infrared radiation-reflective elementis used in association therewith as disclosed in my aforementionedcopending application.

The present transfer compositions are preferably based primarily uponrelatively soft waxes such as beeswax, paraffin wax, microcrystallinewax and the like and mixtures thereof with harder waxes such as carnaubawax, and may contain small amounts of liquid or semi-solid resinousadditives such as polybutene resins to render the compositions moretacky. Small amounts of oils such as mineral oil may also be present inaddition to the coloring matter. The transfer compositions are soformulated as to have sharp melting points, preferably within the rangeof from about F. to about F., so that they melt sharply and transfersubstantially completely when heated.

The following examples illustrate suitable transfer compositions.

Example 1 Ingredients: Percent by weight Carnauba wax 40 Paraffin wax 57Milori blue 3 Example 2 Ingredients:

Carnauba wax 75 Petroleum wax 23 Milori blue 2 Example 3 Ingredients:

Beeswax 35 Paraffin wax 43.5 Carnauba wax 20 Milori blue 1.5

The foregoing compositions are applied to thin flexible foundationsheets by conventional hot metal techniques. The foundation may be paperor a plastic film. The latter is preferred in that it permits completetransfer of the imaging composition to the master sheet, although thesame result may be obtained through the use of paper foundationscarrying a smooth layer of plastic between the paper and the transferlayer. However, the objectives of the present process can also beobtained by means of the partial transfer permitted by an untreatedpaper foundation.

It is not completely clear why the present heat-meltable compositionswill release from the plastic film of the transfer sheet and transfer tothe release surface of the master sheet in the first step, and will thenseparate from the release surface and transfer to the copy paper in thesecond step. It appears that the present compositions form a strongerbond with the release surface the first time they are melted thereonthan they do when they are remelted thereon. Also, the second steptransfer is assisted by the porosity of the copy paper which permits theheat-melted images to impregnate the paper surface and strongly bondthereto upon cooling and separation.

The temperatures generated in the present process, both in the initialmaster-imaging step and the final copyimaging step, are in excess of aminimum temperature of about 150 F. and generally are within the rangeof from about 200 F. to 250 F.'The temperature in the image areas iscontrolled, in the case of infrared radiation, by controlling the speedwith which the master sheet is transported past the radiation source.The longer the dwell time before the radiation source, the higher willbe the generated temperature.

However, it is preferred to use a more intense radiation source or a hotplate in the final copy-imaging step to insure complete transfer of themaster images to the copy sheet. The temperature generated in the finalstep is preferably from to 30 F. in excess of the temperature generatedin the initial step.

Variations and modifications may be made within the scope of the claimsand portions of the improvements may be used without others.

I claim:

1. A continuous thermographic duplicating system for the production ofnumerous copies of original infrared radiation-absorbing images whichcomprises the steps of:

(a) applying such images to one surface of a plastic film master sheet,the opposite surface of which is smooth and substantially impervious tomolten wax;

(b) contacting the said opposite surface with a layer of heat-meltablewax imaging composition which has a sharp melting point within the rangeof from about 80 F. to about 180 F.;

(c) applying infrared radiation to the images to cause them to becomeheated and to generate an imagewise heat pattern which is conductedthrough the opposite surface of the master sheet to melt portions of theheat-meltable imaging composition in contact therewith;

(d) permitting the melted composition to solidify and separating themaster sheet and layer of imaging composition so that the solidifiedportions of the layer remain bonded to the opposite surface of themaster sheet and transfer thereto as duplicate images in areascorresponding to the location of the original images on the othersurface;

(e) contacting the duplicate images with the surface of a copy paper andapplying sufficient heat to melt the duplicate images and cause them toadhere to the surface of the copy paper;

(f) separating the master sheet and the copy paper whereby the duplicateimages remain adhered to the copy paper and transfer substantiallycompletely from the master sheet; and

(g) repeating steps (b) through (f) using the same master sheet with asuccession of copy papers to produce as many duplicate copies of theoriginal images as desired.

2. The system of claim 1 in which the layer of heatmeltable imagingcomposition is present as a continuous layer on a flexible foundation.

3. The system of claim 1 in which the imaging composition comprises amixture of carnauba wax and a soft wax from the group consisting ofbeeswax, paraffin wax and microcrystalline wax.

4. The system of claim 1 in which the heating in step (e) is effected bymeans of infrared radiation.

5. The system of claim 1 in which the succession of copy papers ispresent in the form of a continuous paper web which is subsequently cutinto sheet lengths corresponding to the subject matter of the mastersheet.

6. A continuous thermographic duplicating system for the production ofnumerous infrared radiation-absorbing copies of original infraredradiation-absorbing images which comprises the steps of:

(a) applying such images to one surface of an infraredradiation-reflective plastic film master sheet, the opposite surface ofwhich is smooth and substantially impervious to molten wax;

(b) contacting the said opposite surface with a layer of infraredradiation-absorbing heat-meltable wax imaging composition which has asharp melting point within the range of from about F. to about F.;

(c) applying infrared radiation to the images to cause them to becomeheated and to generate an imagewise heat pattern which is conductedthrough the opposite surface of the master sheet to melt portions of theheat-meltable imaging composition in contact therewith, the infraredradiation striking the unimaged areas of the master sheet beingreflected back by the master sheet and prevented from reaching the layerof imaging composition;

(d) permitting the melted composition to solidify and separating themaster sheet and layer of imaging composition so that the solidifiedportions of the layer remain bonded to the opposite surface of themaster sheet and transfer thereto as infrared radiationabsorbingduplicate images in areas corresponding to the location of the originalimages on the other surface;

(e) contacting the duplicate images with the surface of a copy paper andapplying sufficient heat to melt the duplicate images and cause them toadhere to the surface of the copy paper;

(f) separating the master sheet and the copy paper whereby the infraredradiation-absorbing duplicate images remain adhered to the copy paperand transfer substantially completely from the master sheet; and

(g) repeating steps (b) through (f) using the same master sheet with asuccession of copy papers to produce as many infraredradiation-absorbing duplicate copies of the original images as desired.

7. The system of claim 6 in which the infrared radiation-reflectivemaster sheet has thereon a thin vacuumapplied metallic layer.

8. The system of claim 6 in which the heating in step (e) is effected bymeans of infrared radiation which is absorbed by the duplicate images.

9. The system of claim 6 in which the succession of copy papers ispresent in the form of a continuous paper web which is subsequently cutinto sheet lengths corresponding to the subject matter of the mastersheet.

References Cited UNITED STATES PATENTS 3,148,617 9/1964 Roshkind101149.4

EARL M. BERGERT, Primary Examiner.

M. L. KATZ, Assistant Examiner.

US. Cl. X.R.

